AN ANALYSIS OF THE TEMPERATURE SITUATION AND THE CAUSES OF URBAN HEAT ISLAND IN BEIJING
Xu Zhaosheng Shen Jianzhu Wang Dehui(Institute of Geography, Chinese Academy of Sciences and State Planning Commission of The People's Republic of China)
In this paper, by using the data of seven city climate stations in Beijing which were set up by ourselves from 1982 -1985, and the meteorological data of the suburbs in the same period, we discussed the situation of (mean, maximum and minimum) temperature and the causes of heat island, as the rate of temperature rises and drops and the level of obstruction affects the vaaririation of temperature in the city and its suburbs. Generally, most articles investigated the phenomena of heat island with some days data, maybe three or four days, that obtained from moving observation.So it is difficult to analyse the rate of rising and dropping of temperature in the city and its suburbs, because of the shortage of long period data.On the base of the city climate data from 1982-1985, we discussed the above-mentioned problems. The main results are obtained as follows.1. The phenomena of heat island exist in four seasons of a year, but it is the strongest in the winter, the weakest in the summer, and spring and autumn is in the medium.2. The mean, maximum and minimum temperatures in the city are higher than those in the suburb. The difference between the city and suburb is about 1.2-2.4℃ from Jan.-Dec.for mean temperature.Their difference is a maximum in January of the winter, a minimum in August of the summer. For maximum temperature, city temperature is only 0.4-1.6℃ higher than the suburb from Jan.-Dec. The maximum difference between city and suburb temperature appears in the monthes of spring and autumn, May and September. In the opposite with mean temperature, the difference is a minimum in January of the winter.Although urban temperatures, regardless of mean temperature, maximum minimum temperature, are higher than that of suburb, the difference between the city and suburb minimum temperature is the greatest. Their difference is about 1.4-3.6℃ from Jan.-Dec. As the same as the mean temperature, the difference is a maximum in winter, a minimum in summer.3. The rate of temperature rising and dropping also has a difference between the city and its suburbs. The rate of rising temperature in the city is slower than that in the suburb from March-April. It is opposite from April to May, the rate of temperature in the city is faster than that in the suburb, and the rate of temperature drops faster in the city than in the suburb from September to October and slower in the city than in the suburb from October to November. We found that different rates of temperature rising and dropping between the city and suburb is a reason which causes the formation of urban heat island of Beijing.4. According to the research on the temperature of different distances from the city center, we found that the temperature is decreasing as the distance increases from the city center outwardly. The decreasing amount of temperature is not equal with distance outwardly in different direct ions. The decreasing amount with distance increasing from city center outwardly is smaller eastward or westward than southward or northward, because Beijing city is larger in width in east-west direction than that in south-north direction. This fact indicates that the level of city obstruction is an important factor in causing the formation of urban heat island.